[PATCH 16/16] docs: Add initial documentation for domain support

Atish Patra atishp at atishpatra.org
Fri Oct 2 02:11:35 EDT 2020 

On Thu, Oct 1, 2020 at 9:49 PM Anup Patel <Anup.Patel at wdc.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Atish Patra <atishp at atishpatra.org>
> > Sent: 02 October 2020 04:32
> > To: Anup Patel <Anup.Patel at wdc.com>
> > Cc: Atish Patra <Atish.Patra at wdc.com>; Alistair Francis
> > <Alistair.Francis at wdc.com>; Anup Patel <anup at brainfault.org>; OpenSBI
> > <opensbi at lists.infradead.org>
> > Subject: Re: [PATCH 16/16] docs: Add initial documentation for domain
> > support
> >
> > On Fri, Sep 25, 2020 at 4:30 AM Anup Patel <anup.patel at wdc.com> wrote:
> > >
> > > We add initial documentation for OpenSBI domain support to help RISC-V
> > > platform vendors achieve system-level partitioning.
> > >
> > > Signed-off-by: Anup Patel <anup.patel at wdc.com>
> > > ---
> > >  README.md              |   3 ++
> > >  docs/domain_support.md | 105
> > +++++++++++++++++++++++++++++++++++++++++
> > >  docs/doxygen.cfg       |   1 +
> > >  3 files changed, 109 insertions(+)
> > >  create mode 100644 docs/domain_support.md
> > >
> > > diff --git a/README.md b/README.md
> > > index bd41ba3..03c02fb 100644
> > > --- a/README.md
> > > +++ b/README.md
> > > @@ -225,6 +225,8 @@ Detailed documentation of various aspects of
> > > OpenSBI can be found under the
> > >  * [Platform Documentation]: Documentation of the platforms currently
> > supported.
> > >  * [Firmware Documentation]: Documentation for the different types of
> > firmware
> > >    examples build supported by OpenSBI.
> > > +* [Domain Support]: Documentation for the OpenSBI domain support
> > > +which helps
> > > +  users achieve system-level partitioning using OpenSBI.
> > >
> > >  OpenSBI source code is also well documented. For source level
> > > documentation,  doxygen style is used. Please refer to the [Doxygen
> > > manual] for details on this @@ -278,6 +280,7 @@ make
> > > I=<install_directory> install_docs  [Platform Support Guide]:
> > > docs/platform_guide.md  [Platform Documentation]:
> > > docs/platform/platform.md  [Firmware Documentation]:
> > > docs/firmware/fw.md
> > > +[Domain Support]: docs/domain_support.md
> > >  [Doxygen manual]: http://www.doxygen.nl/manual/index.html
> > >  [Kendryte standalone SDK]:
> > > https://github.com/kendryte/kendryte-standalone-sdk
> > >  [third party notices]: ThirdPartyNotices.md diff --git
> > > a/docs/domain_support.md b/docs/domain_support.md new file mode
> > 100644
> > > index 0000000..fad4f67
> > > --- /dev/null
> > > +++ b/docs/domain_support.md
> > > @@ -0,0 +1,105 @@
> > > +OpenSBI Domain Support
> > > +======================
> > > +
> > > +An OpenSBI domain is a system-level partition (subset) of underlying
> > > +hardware having it's own memory regions (RAM and MMIO devices) and
> > > +HARTs. The OpenSBI will try to achieve secure isolation between
> > > +domains using RISC-V platform features such as PMP, IOPMP, etc.
> > > +
> >
> > May be specify a few other options such as ePMP, SiFive shield as well as you
> > mentioned in the patch commit.
>
> Okay, will add.
>
> >
> > > +Important entities which help implement OpenSBI domain support are:
> > > +
> > > +* **struct sbi_domain_memregion** - Representation of a domain
> > memory
> > > +region
> > > +* **struct sbi_hartmask** - Representation of domain HART set
> > > +* **struct sbi_domain** - Representation of a domain instance
> > > +
> > > +Each HART of a RISC-V platform must have an OpenSBI domain assigned
> > to it.
> > > +The OpenSBI platform support is responsible for populating domains
> > > +and providing HART id to domain mapping. The OpenSBI domain support
> > > +will by default assign **the ROOT domain** to all HARTs of a RISC-V
> > > +platform so it is not mandatory for the OpenSBI platform support to
> > populate domains.
> > > +
> > > +Domain Memory Region
> > > +--------------------
> > > +
> > > +A domain memory region is represented by **struct
> > > +sbi_domain_memregion** in OpenSBI and has following details:
> > > +
> > > +* **order** - The size of a memory region is **2 ^ order** where
> > > +**order**
> > > +  must be **3 <= order <= __riscv_xlen**
> > > +* **base** - The base address of a memory region is **2 ^ order**
> > > +  aligned start address
> > > +* **flags** - The flags of a memory region represent memory type (i.e.
> > > +  RAM or MMIO) and allowed accesses (i.e. READ, WRITE, EXECUTE, etc)
> > > +
> > > +Domain Instance
> > > +---------------
> > > +
> > > +A domain instance is represented by **struct sbi_domain** in OpenSBI
> > > +and has following details:
> > > +
> > > +* **index** - Logical index of this domain
> > > +* **name** - Name of this domain
> > > +* **assigned_harts** - HARTs assigned to this domain
> > > +* **possible_harts** - HARTs possible in this domain
> > > +* **regions** - Array of memory regions terminated by a memory region
> > > +  with order zero
> > > +* **boot_hartid** - HART id of the HART booting this domain. The
> > > +domain
> > > +  boot HART will be started at boot-time if boot HART is a possible
> > > +and
> > > +  assigned for this domain.
> > > +* **next_addr** - Address of the next booting stage for this domain
> > > +* **next_arg1** - Arg1 (or 'a1' register) of the next booting stage for
> > > +   this domain
> > > +* **next_mode** - Priviledge mode of the next booting stage for this
> > > +domain
> > > +* **system_reset_allowed** - Is domain allowed to reset the system?
> > > +
> > Will it be better to keep a bitwise flags for such features ?
> > Does a domain allow modification of PMP regions ?
> >
> > > +The memory regions represented by **regions** in **struct
> > > +sbi_domain** have following additional constraints to align with RISC-V
> > PMP requirements:
> > > +
> > > +* A memory region to protect OpenSBI firmware from S-mode and U-
> > mode
> > > +  should always be present
> > > +* For two overlapping memory regions, one should be sub-region of
> > > +another
> > > +* Two overlapping memory regions should not be of same size
> > > +* Two overlapping memory regions canot have same flags
> > /canot/cannot/gc
>
> Okay, will update.
>
> >
> > > +* Memory access checks on overlapping address should prefer smallest
> > > +  overlapping memory region flags.
> > > +
> > > +ROOT Domain
> > > +-----------
> > > +
> > > +**The ROOT domain** is the default OpenSBI domain which is assigned
> > > +by default to all HARTs of a RISC-V platform. The OpenSBI domain
> > > +support will hand-craft **the ROOT domain** very early at boot-time
> > > +in the following manner:
> > > +
> > > +* **index** - Logical index of the ROOT domain is always zero
> > > +* **name** - Name of the ROOT domain is "root"
> > > +* **assigned_harts** - At boot-time all valid HARTs of a RISC-V
> > > +platform
> > > +  are assigned the ROOT domain which changes later based on OpenSBI
> > > +  platform support
> > > +* **possible_harts** - All valid HARTs of a RISC-V platform are
> > > +possible
> > > +  HARTs of the ROOT domain
> > > +* **regions** - Two memory regions available to the ROOT domain:
> > > +  **A)** A memory region to protect OpenSBI firmware from S-mode and
> > > +U-mode
> > > +  **B)** A memory region of **order=__riscv_xlen** allowing S-mode
> > > +and
> > > +  U-mode access to full memory address space
> > > +* **boot_hartid** - Coldboot HART is the HART booting the ROOT
> > domain
> > > +* **next_addr** - Next booting stage address in coldboot HART scratch
> > > +  space is the next address for the ROOT domain
> > > +* **next_arg1** - Next booting stage arg1 in coldboot HART scratch
> > > +space
> > > +  is the next arg1 for the ROOT domain
> > > +* **next_mode** - Next booting stage mode in coldboot HART scratch
> > > +space
> > > +  is the next mode for the ROOT domain
> > > +* **system_reset_allowed** - The ROOT domain is allowed to reset the
> > > +system
> > > +
> > > +Domain Effects
> > > +--------------
> > > +
> > > +Few noteworthy effects of a system partitioned into domains are as
> > follows:
> > > +
> > > +* At any point in time, a HART is running in exactly one OpenSBI
> > > +domain context
> > > +* The SBI IPI and RFENCE calls from HART A are restricted to the
> > > +HARTs in
> > > +  domain assigned to HART A
> > > +* The SBI HSM calls which try to change/read state of HART B from
> > > +HART A will
> > > +  only work if both HART A and HART B are assigned same domain
> > > +* A HART running in S-mode or U-mode can only access memory based on
> > > +the
> > > +  memory regions of the domain assigned to the HART
> >
> > How about effects on PMP ?
>
> PMP is only accessible to M-mode so S-mode and U-mode can only
> access memory based on PMP configuration which is based on the
> memory regions of domain assigned to the HART.
>
> Is there anything missing ?
>

I meant to ask about the general effects of domain on PMP. I was not
asking to follow up the previous sentence. Let me rephrase.

A child domain can run M-mode only payload where next_mode will be
M-mode. Correct ?
In that case, can it modify PMP ? or what happens if a child domain
next stage running in M-mode tries to modify some pmp configurations ?

> >
> > > \ No newline at end of file
> > > diff --git a/docs/doxygen.cfg b/docs/doxygen.cfg index
> > > dbf8ef9..82f31a7 100644
> > > --- a/docs/doxygen.cfg
> > > +++ b/docs/doxygen.cfg
> > > @@ -795,6 +795,7 @@ INPUT                  = @@SRC_DIR@@/README.md \
> > >                           @@SRC_DIR@@/docs/platform_guide.md \
> > >                           @@SRC_DIR@@/docs/platform_requirements.md \
> > >                           @@SRC_DIR@@/docs/library_usage.md \
> > > +                         @@SRC_DIR@@/docs/domain_support.md \
> > >                           @@SRC_DIR@@/docs/firmware \
> > >                           @@SRC_DIR@@/docs/platform \
> > >                           @@SRC_DIR@@/include \
> > > --
> > > 2.25.1
> > >
> > >
> > > --
> > > opensbi mailing list
> > > opensbi at lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/opensbi
> >
> >
> >
> > --
> > Regards,
> > Atish
>
> Regards,
> Anup



-- 
Regards,
Atish

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